The present invention relates to the art of metal surface treatment. More specifically, the present invention relates to treatment of metal surfaces with a solution comprising a metal ion selected from the group consisting of titanium, zirconium and hafnium ions and mixtures thereof and a poly-alkenylphenol derivative or an acid salt of a poly-alkenylphenol derivative. Optionally, the solution can also comprise a compound selected from the group consisting of thiourea, a derivative of thiourea, tannic acid, a vegetable tannin and mixtures thereof. The treatment imparts improved corrosion resistance and paint adhesion characteristics to the metal surfaces.
The need for applying protective coatings to metal surfaces for improved corrosion resistance and paint adhesion characteristics is well known in the metal finishing and other metal arts. Traditionally, metal surfaces are treated with chemicals which form a metal phosphate and/or metal oxide conversion coating on the metal surface to improve the corrosion resistance and paint adhesion thereof. Also traditionally, the conversion coated metal surface have been rinsed or post-treated with a solution containing a hexavalent chromium compound for even greater corrosion resistance and paint adhesion.
Because of the toxic nature of hexavalent chromium compounds, expensive treatment equipment must be used to remove chromates from plant effluent to prevent the pollution of rivers, streams, and drinking water sources. Hence, although the corrosion resistance and paint adhesion characteristics of conversion coated metal surfaces can be enhanced by an after-treatment solution containing a hexavalent chromium compound, in recent years there have been research and development efforts directed to discovering effective alternatives to the use of such post-treatment solutions. One alternative is provided in an earlier U.S. patent application of Andreas Lindert, Ser. No. 210,910 for "Composition for and Method of After-Treatment of Phosphatized Metal Surfaces" filed on Nov. 28, 1980. Another alternative is provided in U.S. patent application of Andreas Lindert, Ser. No. 490,579, co-filed herewith. It would, however, be desirable to have further improved post-treatment solutions having improved performance characteristics and requiring shorter treatment times.
In accordance with the present invention a novel compostion which is an alternative to hexavalent chromium compound containing solutions is provided for use in post-treatment solutions in a novel process for the post-treatment of phosphatized or conversion coated metal surfaces. Also, the present invention provides a solution and method for treating previously untreated metal surfaces including aluminum, steel and zinc metal surfaces. The solution and method of the present invention provide a coating on the metal surface and are effective to enhance the corrosion resistance and paint adhesion characteristics of a conversion coated or uncoated metal surface whether previously conversion coated or not. Further understanding of this invention will be had from the following disclosure wherein all parts and percentages are by weight unless otherwise indicated.